1. Field of the Invention
The invention relates to the production of aldehydes and more particularly to the use of coatings on solids to effect biphasic hydroformylation, e.g., the vapor phase reaction of lower olefins with hydrogen and carbon monoxide in the presence of a liquid phase heterogeneous catalyst or a liquid phase reaction using an insoluble amorphous coating containing the catalyst on a support in contact with a second liquid phase containing a higher olefin or a solution of the olefin in a hydrophobic solvent.
2. Description of the Invention
Hydroformylation of an olefin to produce a formyl-substituted derivative of the olefin is well-known in the art as an economically attractive method for producing aldehydes which are primary intermediates in the manufacture of alkanols such as n-butanol and the corresponding alkanoic acids. Also important are such end products as 2-ethylhexanol, which is formed from n-butyraldehyde by a sequence of steps including aldoling, dehydration, and hydrogenation by methods which are well-established in the art.
While hydroformylation processes using cobalt carbonyl as the major component of the catalyst have been known and used for many years, systems in which the catalyst comprises rhodium hydrido carbonyl complexed with an organic ligand have been developed more recently and are now favored over the older technology since they can be used under relatively mild reaction conditions and can be controlled so as to yield a product in which the normal isomer of the aldehyde predominates over the branched-chain isomer to a greater extent than has normally been obtained heretofore when using the older methods. It will be understood in this regard that for most industrial purposes, including use as a raw material for production of the corresponding alkanoic acids (by catalytic oxidation of the aldehyde) and also for the production of higher molecular weight alcohol derivatives (as by aldoling, etc.), the normal aldehyde is strongly preferred over the branched-chain isomer. In the case of the butyraldehydes, for example, n-butyraldehyde finds a ready and expanding market whereas isobutyraldehyde has fewer uses and is considered an undesirable by-product. Similarly, in the case of longer-chain aldehydes such as heptaldehyde, the normal isomers can be used to produce high-quality ester-type synthetic lubricants, while the properties of the corresponding branched-chain isomers are such that they have lesser value for such purposes.
Use of the rhodium-containing catalyst systems results in the attainment of an improved normal:iso ratio in the aldehyde products formed in these processes (as compared with the cobalt-based systems), but formation of the branched-chain isomer continues to be a significant economic drawback. By controlling such parameters as carbon monoxide partial pressure, carbon monoxide:hydrogen ratio, etc., it is possible to influence the product distribution somewhat in a favorable direction. A very significant process parameter is also the ratio of ligand to rhodium in the catalyst mixture, it having been discovered that the normal:iso ratio in the product increases with increasing ligand:rhodium ratio. For example, phosphine-type ligands, such as triphenylphosphine, are customarily employed in rhodium-catalyzed hydroformylation systems in proportions such that the ratio of phosphorus to rhodium is at least about 10:1, ranging on upwardly to as much as 1000:1. Ratios lower than about 2:1 have been found to be unsatisfactory. As the phosphorus:rhodium ratio is increased in the systems employing the previously-recognized ligands such as triphenylphosphine, there is a gradual improvement in the normal:iso ratio in the product aldehydes indicative of an equilibrium-type reaction. Thus, normal practice is to use a substantial excess of ligand on the basis of judgement and of the rapidity of catalyst deactivation observed with various ligand:rhodium ratios.
In the prior art processes for hydroformylation of olefins with hydrogen and carbon monoxide, the typical catalysts employed are homogeneous and are dissolved in the liquid phase reaction system to achieve a high rate of reaction and selectivity. For high boiling alkenes (greater than C.sub.5), systems of this type, however, suffer the disadvantage of product separation, catalyst recovery and catalyst regeneration. Liquid phase systems, for example, require additional processing steps and special equipment for separation of dissolved metal catalysts from liquid reaction products, thereby contributing to significant catalyst losses due to handling of catalyst solutions.
In attempts to overcome the inherent disadvantages in the use of homogeneous catalysts, it has been proposed in U.S. Pat. No. 3,733,362 to use heterogeneous catalysts comprising a Group VIII metal and a biphyllic ligand impregnated on an inert solid support such as silica, alumina, silica-alumina, titania, etc., activated carbon, charcoal, graphite, clays, naturally occurring aluminosilicates such as mordenite, chabazite and gmelinite, and synthetic zeolites such as zeolites X, Y, L or J. It has also been proposed to use a solid catalyst comprising a solid inorganic support material and a solid, active catalytic material comprising a polymeric transition metal complex, e.g., rhodium, for the hydroformylation of olefins to produce aldehydes, as disclosed in U.S. Pat. No. 4,504,684. It has been further proposed in U.S. Pat. No. 3,855,307 to Rony et al to use the combination of liquid and solid phase catalysts in a single unitary multiphase catalytic entity in which a liquid phase catalyst is disposed upon porous supports or substrates. The liquid phase catalyst, which is liquid under reaction conditions, comprises a non-volatile and more volatile solvent with a catalytic component such as a metal salt dissolved or dispersed therein. Rony et al reported maximum selectivities to the linear aldehyde (n-butyraldehyde) of 10:1 using supported rhodium and cobalt based metal complexes in a liquid phase of a non-volatile liquid such as butyl benzyl phthalate, diphenyl ether and diphenyl 2-ethylhexyl diphenyl phosphate. See, also, Rony & Roth, J. Molecular Catalysis 1 (1975/76)13. Insoluble heterogeneous hydroformylation catalysts for converting propylene to butyraldehyde have also been proposed by Hjortkjaer et al, J. Molecular Catalysis 6 (1979)405 who supported hydridiocarbonyltris(triphenylphosphine) rhodium I and excess triphenylphosphine on various supports for the hydroformylation of propene at 100.degree. C. under a pressure of 11 atmospheres. Gerritsen et al, J. Molecular Catalysis 9 (1980), pages 139 and 241, further disclose heterogeneous hydroformylation of ethylene and propylene with supported rhodium complexes of the above type dissolved in triphenylphosphine at reaction conditions of 100.degree. C. and 80 psig. Selectivities to the normal isomer, however, were 10:1 with one example yielding a 20:1 normal:iso ratio.
While supported liquid phase catalysts offer a number of advantages over homogeneous hydroformylation processes of the prior art, including product recovery catalyst recycle and catalyst regeneration, they also suffer the disadvantage of low product selectivities of 95%, or less, to the desired linear aldehyde product.